In recent years, an information technology (IT) system is indispensable in business, and it is important to continue the business even in the case of a disability or a disaster. An opportunity loss caused by the IT system stop is enormous, for example, is said to amount to some millions dollar in a banking business and a large company. In view of the background mentioned above, a disaster recovery (hereinafter, refer to DR) system is paid attention, the DR system being structured such as to prepare two sites comprising primary and secondary sites capable of actuating the database, back up business data to the secondary site at a usual time and continue the operation by the secondary site at a disaster time.
In the DR system, each of the primary site and the secondary site is provided with a database (hereinafter, refer to DB) server and a storage apparatus from a usual time. Accordingly, great much cost is required for constructing and maintaining the DR system such as construction and control costs of the primary and secondary sites, a circuit cost and the like. However, it is said that a probability at which the disaster is actually generated is some % in all the disability. Accordingly, in recent years when it is desired to make the business efficient and reduce the cost, an added value is required in the DR system.
As one example of the added value mentioned above, there is a backup system corresponding to Rolling Disaster in which the DR system is highly developed.
The Rolling Disaster means that each of the system constituting elements is gradually broken at different timings at a time when the disaster is generated, in place that the system constituting elements are broken simultaneously. Accordingly, update of the data is transferred from the primary site to the secondary site on and after the disaster is generated, so that there is generated a possibility that a consistency is not secured in the data backed up in the secondary site.
In order to cope with the Rolling Disaster mentioned above, there is known a structure which stores a point in time (PiT) image before the disaster is generated, in addition to a most recent PiT image in the database (for example, Claus Mikkelsen, “The Hitachi NanoCopy Advantage”, pp. 9-11, [online], “searched on Jul. 16, 2004”, via the Internet http://www.hds.com/pdf/wp134_nanocopy.pdf).
This is structured such that the secondary site is provided with a first volume and a second volume, the primary site repeats interruption and recovery of a remote copy by a timer, the secondary site records the remote copy in the first volume at a time of receiving the remote copy, and when the remote copy is interrupted, the secondary site copies the data from the first volume to the second volume after confirming that the primary site has no disability, thereby preparing the PiT image at that time point. When the primary site returns the remote copy, the secondary site writes the date in the first volume. Accordingly, the secondary site always stores most recent generation of backup (the first volume) and one generation anterior backup (the second volume), and even if the writing is executed in the first volume due to the Rolling Disaster, it is possible to return on the basis of the one generation anterior backup stored in the second volume.
Another example which gives the added value of the DR system, there is known a structure which executes a searching process of the DB in addition to the backup, by the secondary site which has a lower load than the primary site (for example, “Oracle Data Guard”, “Overview of Oracle Data Guard Functional Components”, [online], “Searched on Jul. 16, 2004”, via the Internet, http://otn.oracle.com/deploy/availability/htdocs/DataGuardOverv iew.html).
This is structured such that each of the primary site and the secondary site is provided with a database management system (DBMS) and a storage apparatus, and the primary and secondary sites are connected only by a network between servers. Further, the DBMS of the primary site transfers log to the DBMS of the secondary site at the same time of writing the data in the storage apparatus. The DBMS of the secondary site writes the received log in the storage apparatus. Further, in the secondary site, the DB is updated by applying the log written in the storage apparatus to the DB of the secondary site at the time of not executing the operation such as the searching process or the like.